Electrochemical recovery of rare earth metals in molten salts

Abstract

Electrochemical metal extraction in molten salts is the dominant industrial method for production of Rare Earth (RE) metals from their oxides. Two major challenges pertaining to RE metals extraction using this technology are a) low solubility of RE oxides in molten salts and b) carbon monoxide or carbon dioxide generation and possibility of fluorocarbon gas generation. The primary objective of this thesis is to find new methods to overcome the problem of low solubility of RE oxides in molten fluorides in order to increase the RE metal extraction yield from RE oxides. Another objective is to study novel routes in order to prevent CO, CO2 and halogen gas generation in the RE metal production from RE oxide and RE magnet scrap in molten salt electrolysis process. In view of this, a treatment route is suggested for the conversion of RE oxide to RE chloride/fluoride using strong chemical agents. Chapters 2, 3 and 4 investigate the conversion routes for RE oxides as well as RE magnet scrap in both chlorides and fluorides molten salts. Chapter 5 investigates the electrolysis step in which iron as a reactive anode is used, preventing generation of fluorocarbon, CO and CO2 gas in the extraction process. In Chapter 6 a thermodynamic modelling of the fluoride salt using CALPHAD approach is carried out. The phase equilibria and thermodynamics of molten fluorides system can be used for optimal design of RE extraction processes.